NEST-SITE SELECTIONThe Stout-billed Cinclodes is a common and conspicuous inhabitant of the paramo from 3,550 to 4,300 m. In January and April, pairs of cinclodes were actively digging and attending burrows (nesting and roosting) in vertical banks and cliff faces formed by roadcuts. A majority of the burrows seemed to be located in palecolored strata composed of decomposed pumice from past volcanic eruptions, rather than in the darker, dense, alternating layers of paleosol (Fig. I). To verify our initial impressions, we independently categorized the placement of burrows on different sections of the road crossing the northwestern Rank ofthe Ruiz strato cone.In April 1982, Arango censused cinclodes' burrows along the roadcut between Arenales and Aguacerales (3,800 to 4,300 m), and estimated the color, texture. and hardness of the stratum from which the burrow was excavated, as well as its vertical placement on the roadcut. Color was originally classified into one of six categories (ranging from cream-colored to black), However, because Graves later distinguished only "dark" paleosols and "light" pumiceous strata, Arango' s data have been reduced to two categories for statistical com- (Table I). As noted previously, texture and hardness of strata were highly correlated to color. The pale pumiceous layers were porous and friable and eas ily excavated with a trowel. Paleosols were harder and heavier and more difficult to work.In January 1986, Graves counted cinclodes' burrows, and the type of strata (dark vs. light) they were excavated from, along a 2-km section of the MurilloGuali Road (3,900 to 4,100 m) about 6 km east of Aguacerales (Table I). The threat of volcanic eruption prevented the measurement ofburrow placement. This locality is less sheltered from wind and less humid than Aguacerales.Although there were highly significant differences in strata selection between sites (x2 = 74.9, df = I, P < 0.001) these data show that cinclodes in both areas prefer pumiceous strata as burrow sites. Both surveys included abandoned burrows as well as those in use. Roadcuts were constructed in the 1950s and 1960s at Aguacerales, and during the 1970s east of the Rio Guali. Burrows persist for many years until the cliff or bluff face erodes away, thus documenting generations of nestsite selection. We hypothesize that pumiceous strata were chosen not only for ease of excavation, but also because drainage there is better than in paleosols. We note parenthetically that the known distribution of C. excelsior in the northern Andes coincides with volcanically active regions.The majority of burrows were excavated within I m FIGURE I. Section of roadcut on Nevado del Ruiz showing alternating pumiceous strata (pale) and paleosols (dark). The entrances of three cinclodes burrows can be seen in upper pumiceous stratum.
